Postharvest ethephon degreening improves fruit color, flavor quality and increases antioxidant capacity in ‘Eureka’ lemon (Citrus limon (L.) Burm. f.)

External color of citrus fruits is a key factor that affects consumer acceptability, and ethephon has been commonly used to the degreening of citrus fruits in the industry. In this study, the green-peeled ‘Eureka’ lemon fruits were treated with ethephon solution (1000 mg/L), and then stored at 20 °C (RH 85%) for 9 days. The fruit color, flavor and antioxidant capacity were investigated during the degreening process, and the qualities of ethephon-degreened fruits were compared to those of yellowish bagged fruits. The results showed that the postharvest ethephon treatment improved the external color, which was indicated by the increases in the citrus color index (CCI) and chroma (C*), and declines in hue angle (h°) and total chlorophylls. Titratable acidity (TA) was lower than that of bagged fruits after ethephon treatment. Soluble solids content (SSC), SSC/TA ratio and ascorbic acid were decreased slightly, but they were still higher than those of bagged fruits. Although individual organic acid and sugar fluctuated after ethephon treatment, no deleterious effects were observed. The taste-active amino acids increased slightly both in the fruit peel and pulp, and the volatile compounds in fruit peel were obviously increased about 1 time as compared to the untreated fresh fruits. Most interestingly, we found that the antioxidant capacity of the degreened fruits was increased by ethephon degreening treatment, and their DPPH, ABTS, and FRAP values of peels and/or pulps reached the highest at the end of storage. In corroboration this, our data also showed that the enhancement of antioxidant capacity was strongly associated with the increase of total phenolics (r>0.9). Taken together, our study shows that postharvest ethephon degreening treatment is an effective and economical approach to improve the peel color and potentially the internal quality of lemon fruits.